GT3 Limited Slip Diff - is it adjustable?

[Lance Robinson]

I have just acquired a Mk 2 GT3 and a fine machine it is too. Definitely the best car I have had and a much better drive than my last C2!

To my mind though, the LSD is overly stiff. The handbook states: "The differential lock, which was designed for motor sport, may make a slight noise when manouvering and on tight corners."

OK then... but to my mind the diff should not be trying to limit differential rotation unless a decent amount of power is applied. When coasting round tight corners it is completely free, as it should be, but with any drive at all it is trying to do its stuff.

Is mine more severe than it should be and is it adjustable?

[Pork_n_Beem]

They are adjustable if you have a machine shop and know what you are doing, however they do make a noise a yes they do have a static setting.

If you did not have the "pre-load" it would spin up and burn out under hard track loads, the time to worry is when it stops making a noise.

[Dave 321]

I think the diff is designed to lock up more on the overrun than when on the power...

[Kurgen]

Might have a motorsport pack in it, with more drive lock.

Had this fitted to my GT2, makes big difference. (on track)

You have to remove the diff to adjust the lock (not a huge job) The clutches are wet multiplate (like motorbike) and do wear. I was told that on cup cars they rebuild the diff after every race.

Rob

[GuyS.]

Kurgen said:

I was told that on cup cars they rebuild the diff after every race.

No matey, they need rebuilding at roughly the same time as the engine, which is done after about 70 hours.

[Kurgen]

GuyS. said:

Kurgen said:

I was told that on cup cars they rebuild the diff after every race.

No matey, they need rebuilding at roughly the same time as the engine, which is done after about 70 hours.

Fair enough.. was told by Mark Sumpter.

Engine rebuild is a major/expensive job, where as diff rebuild or adjustment is 4ish hours.

Rob

[Lance Robinson]

So do I gather that here was a motorsport option on the diff?? Is this a standard option sheet item or a retrofitting of racing kit?

If not the motorsport one, is the standard item readliy adjustable? No machine shop for me please!!!

[Kurgen]

Lance Robinson said:

So do I gather that here was a motorsport option on the diff?? Is this a standard option sheet item or a retrofitting of racing kit?

If not the motorsport one, is the standard item readliy adjustable? No machine shop for me please!!!

There was no option for motorsport diff. It is a pack of gubbins, which fits in standard housing. The lock can be adjusted once the diff is removed.

Call Fearns, he set my diff.

[GuyS.]

Kurgen said:

GuyS. said:

Kurgen said:

I was told that on cup cars they rebuild the diff after every race.

No matey, they need rebuilding at roughly the same time as the engine, which is done after about 70 hours.

Fair enough.. was told by Mark Sumpter.

Engine rebuild is a major/expensive job, where as diff rebuild or adjustment is 4ish hours.

Rob

makes you wonder how Porsche manage to finish all those 24hr races then !

Edited by GuyS. on Monday 14th May 08:25

[Kurgen]

GuyS. said:

Kurgen said:

GuyS. said:

Kurgen said:

I was told that on cup cars they rebuild the diff after every race.

No matey, they need rebuilding at roughly the same time as the engine, which is done after about 70 hours.

Fair enough.. was told by Mark Sumpter.

Engine rebuild is a major/expensive job, where as diff rebuild or adjustment is 4ish hours.

Rob

makes you wonder how Porsche manage to finish all those 24hr races then !

Edited by GuyS. on Monday 14th May 08:25

Clutches are a wear item, does not mean that car stops functioning.. but the lock (and race cars can run 100% lock with slicks) would be diminished after a 24hr race. On a normal race, one would ensure optimum diff function, for start of race as cost is relatively minimal.

Rob

[GuyS.]

Kurgen said:

Clutches are a wear item, does not mean that car stops functioning.. but the lock (and race cars can run 100% lock with slicks) would be diminished after a 24hr race. On a normal race, one would ensure optimum diff function, for start of race as cost is relatively minimal.

Rob

Thank you for clearing that up for me. Just out of interest, why would anyone want to run 100% lock ?

Guy

[Kurgen]

GuyS. said:

Kurgen said:

Clutches are a wear item, does not mean that car stops functioning.. but the lock (and race cars can run 100% lock with slicks) would be diminished after a 24hr race. On a normal race, one would ensure optimum diff function, for start of race as cost is relatively minimal.

Rob

Thank you for clearing that up for me. Just out of interest, why would anyone want to run 100% lock ?

Guy

Speak to Rancey. (think he said it was a 935, obviously it wanted to plow into the kitty litter until tyre temps were up)

Edited by Kurgen on Monday 14th May 08:53

[Kurgen]

Found it ..

steve rance said:

Kurgen said:

Have had a motorsport diff fitted to my gt2, makes a huge difference to the power delivery.
As you feed the power out of the corner, the diff allows the car about a 1 ft movement before locking up and firing out.

nice bit of kit!

Do you know how it's set up kurg? There are so many mays to set up a diff as they are reversable. ie; a 60/40 diff can be 40 on braking and 60 on power or 60 on braking and 40 on power. Remember that the more lock you have on braking and transition to more pronounced your understeer will be. The best diff I drove had 20 on braking and 80 on power. Not brilliant underbraking but wow, it put the power down! Mike wilds was telling me that he drove a 935 at lemans some time ago and it had a 100% locking diff. Aparently it went straight on most of the time until the tyres warmed up!

[DanH]

Lance Robinson said:

So do I gather that here was a motorsport option on the diff?? Is this a standard option sheet item or a retrofitting of racing kit?

If not the motorsport one, is the standard item readliy adjustable? No machine shop for me please!!!

The standard diffs wears out reasonably quickly (apparently - mine hasn't!). People then tend to replace it with the motorsport one from a cup car or whatever. This is much stronger, but also has more lock which isn't so hot around town.

[Kurgen]

DanH said:

Lance Robinson said:

So do I gather that here was a motorsport option on the diff?? Is this a standard option sheet item or a retrofitting of racing kit?

If not the motorsport one, is the standard item readliy adjustable? No machine shop for me please!!!

The standard diffs wears out reasonably quickly (apparently - mine hasn't!). People then tend to replace it with the motorsport one from a cup car or whatever. This is much stronger, but also has more lock which isn't so hot around town.

Dan, you need to drive it harder!
Are you still weaving around the cones at Bedford?

Rob

[Pork_n_Beem]

These diffs are a bit aggracultural in the way they work, the concept of adjustability is not like a tweek here or there it is more like trying to adjust a fixed damper. You have to change the internals and engineer the pre-load. These components are not cheap, hence the machine shop route

I didn't think you had that in mind.

A locking ration of 25% under power is about the bare minimum for a track car and even though, the diff will always be under pressure to slip under power which wears it out, hence change the oil often.

As soon as the diff gives up and you get inside wheel spin, get the diff rebuilt, by then you won't be getting much growning driving around town.

[DanH]

Kurgen said:

DanH said:

Lance Robinson said:

So do I gather that here was a motorsport option on the diff?? Is this a standard option sheet item or a retrofitting of racing kit?

If not the motorsport one, is the standard item readliy adjustable? No machine shop for me please!!!

The standard diffs wears out reasonably quickly (apparently - mine hasn't!). People then tend to replace it with the motorsport one from a cup car or whatever. This is much stronger, but also has more lock which isn't so hot around town.

Dan, you need to drive it harder!
Are you still weaving around the cones at Bedford?

Rob

haha. Shall I ask that question you keep dodging again?

[Kurgen]

You can ask it, matey..

Although, the answer has no affect on me, and don't want to open a can of worms for somebody else!

Rob